I love it. Mist was one thing that I thought was really lacking in the stalker series.. it could have been done used a lot more. A thick mist like this adds so much atmosphere and makes it challenging in a whole new way. :)
A volumetric mist would be nice but I don't know if it's possible with current tech let alone the x-ray engine. Seeing the mist move and stir as something moved through it just outside the visible range would be awesome.

Perhaps the mist could also affect the players character?
I mean, just like in real life, you could run further in the cold, damp mist than on a 30 Degrees Celcius day...
Or maybe the firerate of your automatic weapons would drop to replicate condensation build-up in the barrel and chamber, perhaps leading to a jam?...